# Requirements for fission

1. Nov 11, 2012

### mitch_1211

So I think, as a rule of thumb that for fission to be possible $\frac{Z^2}{A}$$\geq$47

I want to be able to derive this relationship though..

If a nucleus deforms into an ellipsoid, its surface area can be described by

4$\pi$R2(1+$\frac{2}{5}$$\epsilon^2$ + ...) call this X

And its Coulomb energy can be described as

$\frac{3Z^2}{20\pi\epsilon_0R}$(1-$\frac{1}{5}$$\epsilon^2$ + ...) call this Y

And so ΔBE = X-Y

For fission to occur set ΔBE ≤ 0

Once I've done all this I'm not sure how to get ΔBE in terms of A and Z only. I know R = r0A1/3

thanks

2. Nov 11, 2012

### mitch_1211

I should mention that $\epsilon$ is an arbitrary deformation parameter associated with the ellipsoid and can be factored out

3. Nov 12, 2012

### Staff: Mentor

You can use that formula for R and solve for $\frac{\partial (X-Y)}{\partial \epsilon}=0$.
I would expect that this overestimates the required Z^2/A - if that derivative is negative, the nucleus should not form at all or decay within less than a femtosecond.